System of control



M 1929- H. D. JAMES ET AL 1,729,874

SYSTEM OF CONTROL Filed March 1, 1925 2 Sheds-Sheet l WITNESSES:

INVENTORS 9 I c 2 Henvy D-James and 12 C Easel I ATTORNEY Oct. 1, 1929.H. D. JAMES ET AL 1,729,874

SYSTEM OF CONTROL Filed March 1, 1923 2 Sheets-Sheet 2 o 1 o R122. -02,5 0

a as 5R Fig.2.-

WITNESSES: INVENTORS Hem) D. James and W Hwvy C Nagel ATTORNEY PatentedOct. 1, 1929 UNITED STATES PATENT OFFICE HENRY D. JAMES, OF EDGEWOODPARK, AND HARRY C. NAGEL, F \VILKINSBUBG, PENNSYLVANIA, ASSIGNORS TOWESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OFPENNSYLVANIA SYSTEM OF CONTROL Application filed March 1, 1923.

Our invention relates to rheostats for motor control systems and it hasparticular relation to rheostats as employed in connection. with shuntmotors for starting or regulating the same. i

In the use of rheostats as usually constructed for connection in shuntmotor field circuit-s and the like, the field excitation is initiallymade very high, by the traversal of fulhrating current through the fieldwinding, followed by the introduction of gradually increasing resistancein the circuit to bring the motor up to the required speed. Rheostats ofthis type necessarily have the contact members thereof relatively largeto properly carry the current without appreciable heating, and in someinstances the contact blocks are larger atthe low resistance end of therheostat, and gradually taper off in size as the resistance increases.In either instance, the total amount of copper required in the rheostatis relatively large and expensive.

One object of our invention is to provide a step-by-step rheostat inwhich the current will traverse two parallel paths until such time as apredetermined amount of resistance has been introduced into the circuit,and then will traverse a single series path when the current has beenreduced to a moderate or relatively low value. By thus directing thecurrent along two parallel resistance paths, and then a single seriespath, the resistors can be made of half the current-carrying capacitythat would otherwise be required were the resistors connected wholly inseries relation, and also a considerable saving in copper otherwiserequired in the contact resistor blocks may be effected.

Another object of our invention is to provide a rheostat whereby thefield winding current, during operation of the rheostat, will be variedin fine gradations, thus producing a relatively smooth increase ordecrease in the speed of the motor.

In the accompanying drawings,

Figure l is a semi-diagrammatic view of a rheostat embodying ourinvention, and

Fig. 2 is a partial schematic View of the same.

ends.

Serial No. 622,108.

As shown, the rheostat is provided with two distinct sets 1 and 2 ofstationary con tact members or blocks, the set 1 comprising twoconcentrically related sections 3 and 4 of which a plurality of like andcircumferentially spaced contact members 3 constitute the one section,and a plurality of similar contact members 1 radially spaced therefrom,constitute the other section. The set 2 also comprises two sections 5and 6, consisting of contact members 5 and 6', respectively, which aresimilar in all respects to the corresponding sections of the set 1.

These sets are arranged in two circular paths about a common center, thecontact members 3 and 6, respectively, of the two sets being arranged inthe outer path, leavin equal spaces between their confronting Thecontact members 1 and 5 of the sets are similarly arranged in the innerpath, except that contact members 4 are in staggered or alternaterelation to contact members 3, and contact members 5 are in similarrelation to contact members 6, for a purpose to be set forth. Concentricwith the sets of contact members is arranged an annular contact memberor ring 7, which serves as one terminal of the rheostat.

In the rheostat, there are three sets of resistors required, the one set8, corresponding to contact members 3 and t, being connected at one endto the first contactmember 9 oi? section 3 and at its other end tointermediate contact member 10 of the same section. A second resistor11, correspond ing to the upper portions of contact members 5 and 6, isconnected at one end to the first contact member 12 of section 6, and atthe other end to the intermediate contact member 13 of the same section.The resistors 8 and 11 are arranged in parallel re lation, one end ofeach being connected to the same terminal 14;, the other commonconnection being described later. The third or series resistor 15 isconnected at one end to the last contact member 16 of section 3, by atap 17,. (shown by dot and dash line) and at its other end to theresistor 11 of which it virtually is a. continuation.

The parallel resistors 8 and 11, are each divided at equidistant pointsinto a plurality of lesser resistance units or substantially equalvalues, tie ends of successive units of the resistor 8 being alternatelyconnected to successive contact members in sections 3 and 4. Similarly,the ends of successive units of resistor 11 are alternately connected tosuccessive contact members of sections 5 and 6, between contact members12 and 18. In the case or" resistor 15, equivalent resistance units aresubdivided into parts of substantially equal resistance value, and thesuccessive taps are connected in alternation to successive contactmembers of the sections 6, l, 3 and 5, as most clearly shown in Fig. 2.

The series resistor 15, considered in detail, is provided with thefollowing alternate connections, a tap 21 to contact member 22 ofsection 6: a tap 23 (shown by dotted line in Fig. 1) to contact member2% 01 section 4::

a tap 25 (shown by dot and dash line in Fig.

1) to contact member 26 of section 3, and a tap 27 to contact member 28of section 5. in completing the internal connections, contact members 10and 2 1 of sections a are connected to oneanot-her "y a tap 31 which, inturn, is connected to contact member 32 of section 3 by a tap 33.

Pivotally mounted on a centrally disposed post 34 is an'operating memberor arm 35, of conducting material, provided near one end with brushes 36and 37 for operating over the contact members of sections 3 and 4,respectively. A pair of similar brushes 38 and 39 are provided near theother end of the arm 35 for operating on the contact members of sections6 and 5, respectively. The contact brushes 36 and 37 are illustrated asplaced one-iiourth the width of a single contact block ahead of theother brushes 38 and 39 to afford relatively fine variations of resistance, as hereinafter explained. The arm 35 is further provided withbrushes Q0 and ll for operating over the annular contact member or ring7, which constitutes one terminal of the rheostat.

In practice, a shunt field winding 42 is connected to the terminal 1eand the other terminal or contact ring 7 to the opposite side oi? tneexcitation circuit, as is customary.

Such being the case, with the arm 35 positioned as shown, the initialcircuit entends from the positive terminal of the source of energy, ordynamo-electric machine (not shown) through the field winding 42 to thejunction post or terminal 1 where the circuit divides, one branch,including the first contact members 12 and 51 of sections 6 and 5,respectively, and brushes 33 and 39 to the arm 35, brush and contac-uring 7 to the negative supply conductor 43. The other branch includesconductor 44, contact members 9 and 20 and brushes 36 and 37 of the armand negative conductor l3 by way of brush &1 and contact ring 7.

In operation, when the arm 35 is moved in a clockwise direction, "forexample, until brush 38 rests in the middle of the second contact memberin sect-ion 6, the brush 39 then bridges the gap between the first twocontact members of section 5. Without detailed tracing of circuits, itwill be apparent that certain parallel paths are thus provided throughthe initial sections of each of the parallel-related resistors 3 and 11to insert a relatively small amount of resistance in the field windingcircuit, as. will be more clearly understood by inspection of Fig. 2.

By reason of the staggered arrangement of the contact members, 3 and 4,as well as 5' and 6, the variation in the eiiective resist-- ance valuesof the circuit is made very gradual. This result is caused by theprogressive shifting of the active connections from one resistor tap toanother, alternately by the brushes 38 and 39 in the one case, and bythe brushes 36 and 37 in the other. I

Moreover, as mentioned above, the brushes and 39 are advanced inposition with respectto the brushes 36 and 37, by a distance of onequarter that of the width of a single contact block. From thisconstruction, it will be evident that the effect of the resistancevariation, by means of brushes 38 and 39, will occur alternately withrespect to the effect produced by the brushes 36 and 37. By this means arelatively fine variation of resistance -is produced by reason of thealternating action of the brushes 38 and 39 with respect to resistor 11,the similar action of brushes 36 and 37 with respect to resistor 8, andin addition thereto, the combined and relative action of the two sets ofbrushes.

As the arm 35 is advanced around toward the ends of the two parallelresistors 8 and 11, the action as described is repeated, wherebyadditional small resistance units are gradually inserted in circuit, aswill be evident from an inspection of Fig. 2. By the time sufiicientresistance has been inserted in the field winding circuit, to reduce thecurrent to a desirably low value and permit the use of the single seriesresistor 15 without danger of overheating, the said series resistor isgradually introduced into the circuit. This change becomes effectivewhen the arm 35 is further advanced so that the brushes 38 and 39thereof come into engagement with contactbloclrs 22 and 23,respectively, and the brushes 36 and 37 thereof come into engagementwiththe contact members 32 and 24, respectively. At this time the first unitof the series resistor 15 is inserted in series relation with the otheror parallel-related resistors 8 and 11.

As the arm 35 is further advanced, other units of the series resistor 15are gradually introduced into circuit in accordance with the previouslydescribed method of operation. During the time that the single resistor15 is being utilized, the entire resistors 8 and 11 are activelyemployed. This effect is ob tained by the permanent connection of thelower end of resistor 11 through conductor 23 to contact member 24,which, in turn, is connected to the lower end of resistor 8 (Fig. 2). Bymeans of the use of the above-described quarter resistance units, takenwith the staggered relation of the corresponding sets of contactmembers, a very line variation of current is effected during the latterpart of the field-regulating period.

lVe have thus provided a rheostat embodying two parallel resistors to betraversed when the current value is high, and a single resistor when thecurrent value is sutficiently low. In addition thereto, a very fine orgradual variation ot current is provided under all conditions, by reasonof the peculiar relative posiions and connections of the variouselements of the rheostat.

Vhile we have shown and described a prefer-red embodiment of ourinvention, change in, or substitution of various parts, theirarrangement and cooperation, may be made within the scope of theinvention set forth in the appended claims.

\Ve claim as our invention:

1. A rheostat comprising a plurality of contact members arranged in acircular path, a plurality of resistors disposed in parallelcircuitrelation and connected alternately at intervals to said contact members,and a centrally disposed member adapted to operate over said contactmembers to alternately vary the effective resistance values of saidresistors.

2. A rheostat comprising plural sets of contact members, each arrangedin a circular path, a plurality of parallel resistors each havingintermediate points corresponding to certain resistance values connectedin alternation to certain of said contact members and another resistorin series with the parallel resistors and having intermediate pointscorresponding to small resistance values alternately connected to otherof said contact members, and a member adapted to operate over thecontact members to vary the effective resistance values of saidresistors.

3. A rheostat comprising plural sets of contact members arranged in acircular path and in relatively staggered relation, a plurality ofparallel-related resistors each connected to a plurality of said contactmember sets, another resistor connected to other of said contact membersand in series relation to the first-named resistors, and a movable armadapted to operate over the contact members to vary the effectiveresistance values of said resistors.

4. In a rheostat, in combination, a plurality of resistors connected inparallel-circuit relation, a plurality of contact members disposed instaggered relation on opposite sides of the resistors, said contactmembers being electrically connected to the respective resistors, asingle resistor connected in series-circuit relation with theparallel-connected resistors, staggered contact members electricallyconnected to the single resistor, and movable means for engaging thecontact members for varying the effective length of the resistors.

5. In a rheostat, in combination, a plurality of resistors connected inparallel-circuit relat-ion, a double row of contact members disposed instaggered relation, said resistors being electrically connected atintervals and alternately to the contact members of the different rows,a single resistor connected inseries-circuitrelationtotheparallel-connected resistors, saidseries-connected resistor being electrically connected at intervals andalternately to the contact members, and a rotatable contact memberdisposed to engage simultaneously the contact members connected to theparallel resistors to vary the eflective length of the resistors.

6. In a rheostat, in combination, a plurality of sets of contactmembers,said sets compris ing a plurality of concentrically disposed rows ofspaced contact members, a resistor element electrically connected atpredetermined intervals and alternately to the contact members of thedifferent rows in a set, said resistors being connected inparallelcircuit relation, a single resistor connected in seriescircuitrelation to the parallel-connected resistors, said resistor beingalternately connected to the contact members of the different sets, anda movable contact member disposed to engage the contact member of eachset to vary the effective length of both parallel resistors and theseries resistor.

7. In a rheostat, in combination, a plurality of resistors connected inparallel-circuit relation, a plurality of sets of contact memberssymmetrically disposed about a common center, said sets comprising aplurality of rows of staggered contact members disposed in concentricrelationship, the contact members of the rows of the sets beingalternately connected at intervals to the resistors, a single resistorconnected in series-circuit relation to the par a llel-connectedresistors, said single resistor being alternately connected to thecontact members of each set, and a movable-contact member having aplurality of arms disposed to engage the contact members of each set forconcurrently varying the effective length of the resistors.

8. In a rheostat, in combination, a plu rality of resistors connected inparallel-circuit relation, a single resistor connected in series-circuitrelation with the parallel-connected resistors, a plurality of sets ofcontact members electrically connected to the resistors, said setscomprising a plurality of concentrically disposed sections, the contactmembers in each section being staggered with respect to the contactmembers of the other section, and a rotatable member having armsengaging the contact members of each set for simultaneously varying thelengths of the resistors.

In testimony whereof, We have hereunto subscribed our names this 21stday of February, 1923.

HENRY D. JAMES. HARRY C. NAGEL.

